The present invention relates to improvements in track surveying.
In U.S. Pat. No. 3,643,503 filed Apr. 7, 1969, entitled "Track Surveying Method and Apparatus" and application Ser. No. 813,855, filed April 9, 1969 and abandoned in favor of Ser. No. 243,619, filed April 13, 1972, entitled "Track surveying", for instance, of which the present inventor is a joint inventor, track-measuring cars are disclosed which continuously measure and record parameters characteristic of the track condition, such as track gage, superelevation, curvature, grade, etc. Such surveys are designed to establish the safety of the track for given train speeds and determine when track maintenance work is required to bring the track back to the desired norm.
In modern, high-speed track maintenance operations, it is essential to determine the locations where track correction work must be done, and it has been proposed to use computers to evaluate signals characteristic of given measured track conditions, such as superelevation, grade and alignment. For instance, a norm may be established for each condition, i.e., curvature, superelevation, track gage, grade, these conditions may be continuously measured as a surveying car moves over the track, and deviations from the norm may be measured and fed to a computer which will determine when the track section falls below a given norm by counting the number of deviations in this section. While a variety of surveying methods have been tried, it has not been possible to set up a single characteristic value which generally indicates the entire track condition and is determinative of the safety of the track.
It is accordingly a primary object of the present invention to provide a railway track surveying apparatus which uses a single characteristic datum fully reflective of the track condition so that the quality of the track is established by this single parameter or signal.
This and other objects of this invention are accomplished by using as datum the acceleration changes caused by varying local track conditions in the track section being surveyed. The data are related to an assumed uniform speed of a vehicle passing over the track section and they are totalled to produce a parameter or signal characteristic of the track section condition, which signal or parameter is compared with a comparison parameter or signal characteristic of a track condition norm.
It has been found that this single datum related to the acceleration changes actually fully reflects all factors responsible for the quality of the track.
It is preferred to establish data corresponding to the acceleration changes in two mutually perpendicular planes, for instance one defined by the track and the other one perpendicularly extending in the direction of the track. The signals or parameters are separately measured in the two planes, preferably electrically or electronically, and then combined into a characteristic datum, preferably by a vector sum.
The acceleration changes may be measured directly, i.e., by an accelerometer mounted on a car moving over the track at a controllable and measurable speed.
It is also possible, however, to determine the acceleration changes indirectly without using a car with an accelerometer. For instance, changes in a parameter characteristic of successive portions of the track section may be measured, for instance the radii of successive circular arcs which are assumed to form the continuous track section. In this case, the faulty condition of the track section is considered as a succession of curves of the same mathematical function, for instance a series of successive circular arcs. A parameter of these successive curves and the changes in this parameter are measured, and the corresponding acceleration changes of an imaginary vehicle running over the track section is derived from these measurements and evaluated as though the acceleration changes themselves had been measured.